1. Field of the Invention
The invention relates to a method for the preparation of polysaccharide derivatives by reacting at least a saccharide, an acid, which also acts as catalyst, and optionally a polyol at elevated temperature.
2. Description of the Related Art
A method of this type is disclosed in U.S. Pat. No. 3,766,165. More particularly, in said American patent a method is described for the preparation of polysaccharide derivatives, in which method d-glucose or maltose, as saccharide, is reacted in the molten state at a temperature of 140.degree.-295 .degree. C. and under highly reduced pressure in the presence of a catalytic amount of at most 10 mol % of a "food grade" polycarboxylic acid, for example citric acid, in the absence of water, with the proviso that the water produced during melting and polymerisation is removed immediately. A polyol such as sorbitol can also be used in the abovementioned reaction.
European Patent 404,227 describes a method which can be carried out continuously, with which method the desired polysaccharide product can be obtained both within a short time and without the use of vacuum or the apparatus required to maintain vacuum conditions. To this end the reactants, in the form of a mixture of at least a saccharide, a polyol and a "food grade" polycarboxylic acid are fed through a worm shaft reactor or extruder operating at elevated temperature and under elevated pressure, a reaction product at a temperature of 140.degree.-300.degree. C. being obtained.
Both the method according to U.S. Pat. No. 3,766,165 and the method according to European Patent 404,227 require the use of a dry pulverulent reaction mixture as starting material. In European Patent 404,227 it is also stated that the starting material used in the form of a powder usually has a particle size of less than 3 mm and preferably of 0.05-1 mm.